Recently, an increasing number of highly-integrated and high speed Large Scale Integrated (LSI) circuits is in demand. Thus, design rules of semiconductor elements constituting the LSI circuits are increasingly miniaturized. Such miniaturization requires further decreasing the thickness of a gate insulating film used in a CMOS device, which creates a need for the gate insulating film to be made of a material having high permittivity. In addition, there is a need to increase the number of capacitors used in Dynamic Random Access Memories (DRAMs) or the like. There is also a need to improve a permittivity of a dielectric film used in the capacitors. In addition, a flash memory is required to have a further improved reliability. As such, the gate insulating film formed between a control gate and a floating gate is required to have a high permittivity.
An oxide material such as a zirconium oxide (ZrO2) film is being studied as a high-permittivity material which is adaptable to address the above requirements. The zirconium oxide film is formed by a chemical vapor deposition (CVD) (or a metal organic chemical vapor deposition (MOCVD)) using an organic metal material. In addition, as a method of forming the zirconium oxide film, there is proposed an ALD process which alternately supplies tetrakisethylmethylamino zirconium (TEMAZ) used as a raw material gas (precursor) and an O3 gas used as an oxidant gas.
An in-plane uniformity of a metal oxide film such as the zirconium oxide film, which is obtained by the existing ALD process is 3 to 10%. Although the in-plane uniformity of the metal oxide film in the existing LSIs is sufficient with 3%, there is a need for an in-plane uniformity of less than 3% in consideration of miniaturization of future LSIs.
However, in the existing ALD process, the in-plane uniformity is hardly lower than 3%. Deterioration of the in-plane uniformity is drastically manifested when an oxidizing power of an O3 gas is strengthened to make the metal oxide film denser. For example, assuming that a concentration of the O3 gas is increased to strengthen the oxidizing power thereof, the O3 gas having the increased concentration may oxidize ligands in addition to the precursor adsorbed onto a wafer.
When an organic metal is used as the precursor, the ligands become organic ligands such as CH3 or C2H5. Oxidation of the organic ligands generates a H2O or COx gas. In addition, if nitrogen is contained in the organic metal, a NOx gas may be further generated.
In particular, the H2O gas inactivates the O3 gas. As such, a central portion of the wafer is hardly oxidized, thus causing the metal oxide film formed on the wafer to be thick at a periphery of the wafer and thin at the central portion thereof.